As described in co-pending, commonly assigned U.S. patent application Ser. Nos. 09/173,797 and 09/174,074 both filed Oct. 16, 1998, the disclosures of which are incorporated by reference herein, sheet-like elements for use in microelectronic devices can be fabricated and/or assembled while the sheet-like element is held under tension and a frame. For example, a sheet for forming microelectronic connection components may incorporate dielectric layer such as a polyimide sheet. The polyimide sheet may be attached to a frame using an adhesive. The frame may be made of a relatively rigid material having a known, predictable coefficient of thermal expansion such as glass, quartz, or molybdenum. While the sheet is held in tension, features such as metallic leads, contacts and the like can be formed on the surfaces of the sheet by additive processes such as electroplating and/or subtractive processes such as etching. The sheet, with the features thereon, can be aligned with a microelectronic element such as a semiconductor wafer or an assemblage of discrete chips while the sheet is maintained on the frame. Because the sheet is maintained in tension by the frame, and because the frame has known, predictable thermal expansion properties, all of the features on the sheet can be maintained at precise locations relative to one another. The features on the sheet can be precisely aligned with features on the microelectronic element.
As disclosed in certain embodiments of U.S. Pat. No. 5,518,964, the disclosure of which is also incorporated by reference herein, leads can be fabricated on other supports such as dielectric bodies or semiconductor elements so that each lead has one end permanently anchored to the support and another end releasably attached to the support. The support, with the leads thereon, can be engaged with a microelectronic element so that the second ends of the leads are connected to contacts on the microelectronic element, whereupon the support is moved away from the microelectronic element to bend the leads. During this process, the releasable attachments to the support are detached.
As described in certain embodiments of co-pending, commonly assigned U.S. patent application Ser. No. 09/020,750 filed Feb. 9, 1998 and Ser. No. 09/195,371 filed Nov. 18, 1998, the disclosures of which are hereby incorporated by reference herein, a releasable lead structure can be made by providing a lead such as a metallic lead overlying a surface of a dielectric layer and exposing the surface, with the leads thereon, to an etchant such as an oxidizing plasma which attacks the dielectric but which does not substantially attack the material of the lead. The etchant removes the dielectric in areas not covered by the leads. Also, the etchant begins to remove material beneath the leads, starting at the edges of the leads and progressing inwardly from the edges of the leads toward the center. The etching process is stopped before the dielectric has been completely removed beneath all portions of the lead. This leaves the lead connected to the dielectric layer by a relatively small connecting element having an area smaller than the area in the horizontal plane of the lead. The process can be used to provide such small connecting elements as releasable connections at the second ends of the leads in structures such as those taught in the ""964 patent.
The present invention provides certain enhancements to these processes.
One aspect of the invention provides a connection component for making microelectronic assemblies. The apparatus according to this aspect of the present invention preferably includes a structural layer having a first surface, a plurality of conductive leads each having a first end and a second end overlying the first surface of the dielectric structural layer, the first ends of the leads being permanently connected to the structural layer. Preferably, an adhesive is disposed between the second ends of the leads and the structural layer to form connections between the second ends of the leads and the structural layer. The connections desirably have areas smaller than the areas of the second ends, and the second ends of the leads may be releasably attached to the structural layer by the connections. Connection components according to this aspect of the invention can be used in a manner similar to the components of the aforementioned patents and applications. The use of the adhesive layer facilitates fabrication of the component.
The adhesive may extend between the first ends of the leads and the structural layer and forms anchors having areas larger than the areas of the second ends. The structural layer can include either a dielectric layer juxtaposed with the adhesive or a metallic layer. The component preferably further includes a frame overlying portions of the structural layer, the adhesive retaining the structural layer in engagement with the frame, the frame holding the structural layer in tension. Here again, use of the same adhesive layer to hold the leads and frame facilitates fabrication of the component.
A further aspect of the present invention provides a in-process component for making electronic connection components. The in-process component preferably includes a frame having structure defining an aperture and a sheetlike composite element including a structural layer having oppositely-directed first and second surfaces. A first adhesive layer desirably overlies the first surface of the structural layer. The composite element preferably includes peripheral portions overlying the structure of the frame and a central portion aligned with the aperture. Desirably, the adhesive layer extends into the peripheral portions and secures the structural layer to the frame. The adhesive layer also extends into the central portion of the composite element. The structural layer may include a dielectric layer. Desirably, the component further includes a metallic layer overlying the central portion of the composite element and secured to the structural layer by the adhesive layer. The in-process component may further include a second adhesive layer overlying the second surface of the structural layer, and may also include a metal layer overlying the second adhesive layer. The in-process component can be used, for example, to make connection components as discussed above.
Yet another aspect of the present invention provides a method of making a connection component with releasable leads. The method according to this aspect of the present invention preferably includes the steps of providing a structural layer and elongated leads having first and second ends overlying a first surface of the structural layer. Desirably, an adhesive is disposed between the structural layer and the second ends of the leads. The adhesive is preferably etched with an etchant which attacks the adhesive but does not substantially attack the leads so as to partially remove the adhesive beneath the second ends of the leads to thereby form connections having areas smaller than the areas of the second ends of the leads. Preferably, the adhesive is provided as a layer on the structural layer. A layer of metal is desirably provided overlying the structural layer and the layer of metal is selectively etched to form leads. An electrically conductive seed layer is preferably provided on the layer of adhesive and the leads are selectively plated onto the seed layer. The seed layer is then desirably removed except in the regions beneath the leads. A frame may also be provided to define an aperture such that the structural layer extends across the aperture, and the adhesive layer extends between the structural layer and the frame. The structural layer may then be secured to the frame.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.